diff --git a/trisquel-automatic-netinstall-qemu/.gitignore b/trisquel-automatic-netinstall-qemu/.gitignore
index 720569e..0deb0f6 100644
--- a/trisquel-automatic-netinstall-qemu/.gitignore
+++ b/trisquel-automatic-netinstall-qemu/.gitignore
@@ -14,6 +14,7 @@
 /grub/**
 /grub.iso
 /Makefile
+/preseed.cfg
 /preseed.img
 /rootfs.img
 /rootfs.img.tmp
diff --git a/trisquel-automatic-netinstall-qemu/Makefile.am b/trisquel-automatic-netinstall-qemu/Makefile.am
index c261f4a..3303d7f 100644
--- a/trisquel-automatic-netinstall-qemu/Makefile.am
+++ b/trisquel-automatic-netinstall-qemu/Makefile.am
@@ -54,6 +54,10 @@ grub/boot/grub/grub.cfg: Makefile grub.cfg
 grub.iso: Makefile grub/boot/linux grub/boot/initrd.gz grub/boot/grub/grub.cfg
 	grub-mkrescue -o $@ grub
 
+preseed.cfg: preseed.cfg.tmpl
+	sed 's#\@MIRROR_HTTP_PROXY\@#$(MIRROR_HTTP_PROXY)#g' \
+		preseed.cfg.tmpl > $@
+
 preseed.img: Makefile preseed.cfg
 	dd if=/dev/zero of=$@.tmp count=2048
 	mkfs.vfat --mbr=y -n MEDIA $@.tmp
diff --git a/trisquel-automatic-netinstall-qemu/configure.ac b/trisquel-automatic-netinstall-qemu/configure.ac
index f5d792a..43f31ea 100644
--- a/trisquel-automatic-netinstall-qemu/configure.ac
+++ b/trisquel-automatic-netinstall-qemu/configure.ac
@@ -22,6 +22,7 @@ AC_PROG_MKDIR_P
 AM_INIT_AUTOMAKE([foreign])
 
 AC_SUBST([ENABLE_KVM], [])
+AC_SUBST([MIRROR_HTTP_PROXY], [])
 AC_SUBST([TRISQUEL_ROOTFS_SIZE], [])
 AC_SUBST([TRISQUEL_NETINSTALL], [])
 
@@ -33,6 +34,21 @@ AC_ARG_ENABLE(kvm,
 
 AM_CONDITIONAL( [WANT_KVM], [test x"$kvm" = x"yes"])
 
+AC_ARG_WITH(
+  [mirror-http-proxy],
+  [AS_HELP_STRING(
+    [--with-mirror-http-proxy=URL],
+    [URL to the mirror HTTP proxy (default: not set (no mirror)).
+     The proxy configuration is then used during both the netinstall
+     installation and after as well (it's added to /etc/apt/apt.conf).
+     The chosen URL should be reachable from QEMU. As an example, if
+     you use the apt-cacher-ng default configuration and make it
+     listen on localhost, you should use http://10.0.2.2:3142 because
+     localhost becomes 10.0.2.2 with the current QEMU configuration
+     and because the port 3142 is the default port for apt-cacher-ng.])],
+  [MIRROR_HTTP_PROXY=$withval],
+  [MIRROR_HTTP_PROXY=])
+
 AC_ARG_WITH(
   [--with-trisquel-target-rootfs-size],
   [AS_HELP_STRING(
@@ -130,3 +146,6 @@ AS_IF([test x"$kvm" = x"yes"],
       [echo "- Kvm: disabled"])
 echo "- Trisquel netinstall path: $TRISQUEL_NETINSTALL"
 echo "- Trisquel target rootfs size: $TRISQUEL_ROOTFS_SIZE"
+AS_IF([test x"$MIRROR_HTTP_PROXY" = x""],
+      [echo "- Trisquel mirror http proxy: disabled"],
+      [echo "- Trisquel mirror http proxy: $MIRROR_HTTP_PROXY"])
diff --git a/trisquel-automatic-netinstall-qemu/preseed.cfg b/trisquel-automatic-netinstall-qemu/preseed.cfg.tmpl
similarity index 97%
rename from trisquel-automatic-netinstall-qemu/preseed.cfg
rename to trisquel-automatic-netinstall-qemu/preseed.cfg.tmpl
index 31a8c33..fe13cc2 100644
--- a/trisquel-automatic-netinstall-qemu/preseed.cfg
+++ b/trisquel-automatic-netinstall-qemu/preseed.cfg.tmpl
@@ -34,7 +34,7 @@ d-i netcfg/get_hostname                           string   test
 d-i mirror/country                                string   manual
 d-i mirror/http/directory                         string   /trisquel
 d-i mirror/http/hostname                          string   mirror.fsf.org
-d-i mirror/http/proxy                             string
+d-i mirror/http/proxy                             string   @MIRROR_HTTP_PROXY@
 popularity-contest popularity-contest/participate boolean  false
 
 # Partitioning